This is an application to study psychophysiologic stress, exercise, and autonomic control: specifically, the impact of aerobic exercise conditioning on blood pressure variability (BPV) responses to psychological and physical stressors. It is based on a research program which explores the relationships among psychological/behavioral characteristics such as anxiety, hostility, depression, and physical conditioning, the central and autonomic nervous systems, and the cardiovascular and respiratory systems. It derives from a model which holds that autonomic control of the heart serves a buffering or inhibitory function over oscillations in blood pressure, which recent research in vascular biology and dynamics suggests may have pathogenic effects on the endothelium, in the case of atherogenesis, and on plaque stability, in the case of catastrophic cardiac events. Moreover, BPV appears to be a risk factor for cardiovascular disease independent of mean arterial pressure. This model suggests that increasing autonomic control of the heart, as measured by heart period variability (HPV), will result in reduced BPV responses to challenge, an effect which we have documented in a small, cross-sectional study of well- and poorly conditioned normal subjects. These findings suggest that one mechanism by which physical exercise promotes reduced risk of heart disease may be through the dampening of BPV responses to challenge and that this dampening is a function of the degree of HPV. While these findings are suggestive, the cross-sectional nature of this study and the small number of subjects limit the conclusions to be drawn. Accordingly, this application proposes a larger, longitudinal study of the effect of aerobic conditioning of BPV responses to challenge and during 24-hour ambulatory BP monitoring, using students U.S. Army ROTC Empire Regiment, with headquarters at St. John's University. In this study, sedentary ROTC recruits will be tested for BPV responses to challenge and 24-hour ambulatory BPV both before and after random assignment to either 1) a 16 week program of aerobic conditioning or 2) a 16 week program of strength training only. After the post-training set of tests, all subjects will undergo a period of deconditioning after which they again will be tested. A series of hypotheses will test the impact of aerobic conditioning on autonomic control of the heart, BPV responses to challenge, mood, and BPV throughout the day.